Dermal layer analyte sensing devices and methods

ABSTRACT

Provided are dermal sensors and dermal sensor applicator sets to insert at least a portion of a dermal sensor into a dermal layer of a subject, as well as methods of making and using the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/471,867, filed Mar. 28, 2017, which is a continuation of U.S. patentapplication Ser. No. 14/108,964, filed Dec. 17, 2013, now U.S. Pat. No.9,636,060, which claims the benefit of and priority to U.S. ProvisionalApplication No. 61/738,776, filed Dec. 18, 2012, all of which areincorporated by reference herein in their entirety for all purposes.

FIELD

The subject matter described herein relates to devices and methods forthe performance of in vivo analyte sensing in a subject.

BACKGROUND

The detection of the level of glucose or other analytes, such aslactate, oxygen or the like, in certain individuals is vitally importantto their health. For example, the monitoring of glucose is particularlyimportant to individuals with diabetes. Diabetics may need to monitorglucose levels to determine when insulin is needed to reduce glucoselevels in their bodies or when additional glucose is needed to raise thelevel of glucose in their bodies.

Devices have been developed for the in vivo continuous monitoring ofanalytes such as glucose in bodily fluid such as in the blood stream orin interstitial fluid over a period of time. These analyte measuringdevices include in vivo analyte sensors that are positioned in vivo,i.e., below a skin surface of a user in a blood vessel or in thesubcutaneous tissue of a user during the testing.

Blood vessel sensors are more invasive than subcutaneous sensors, buthave the advantage of providing analyte concentrations directly from theblood. Subcutaneous analyte sensors are therefore used, but they toohave certain limitations. For example, the insertion of the analytesensor in the subcutaneous tissue results in skin/tissue trauma thatcauses immunological response that can cause inaccurate sensor readings,at least for a period of time. For example, in the case of glucosesensors, the trauma may cause an over-consumption of glucose in thepositioned sensor vicinity by erythrocytes released by localizedbleeding. Further, the glucose response from a subcutaneously positionedsensor lags the response of a venous-positioned sensor, primarily due toa physiological lag between subcutaneous and venous glucose.

It would therefore be desirable to have devices and methods that addressthese issues and that could accurately monitor analyte levels, such asglucose, in areas of the body other than blood vessels or thesubcutaneous tissue. Analyte sensors, applicators for inserting them,and methods of making and using are described that provide benefits ofblood vessel and subcutaneous analyte sensors without their keylimitations.

SUMMARY

Provided herein are embodiments of in vivo analyte sensors and in vivosensor applicator sets that insert at least a sensing portion of an invivo analyte sensor into a subject. Also provided are embodiments ofmethods of using the sensor applicator sets to insert a sensing portionof an in vivo analyte sensor into a subject, and methods of determiningin vivo analyte presence and concentration using the in vivo analytesensors. Although these embodiments will be described mainly withrespect to a dermal sensor inserted into a dermal layer of a subject, itshould be noted that the sensors can be used in other tissue as well.Many of these dermal embodiments have the conveniences and advantages ofbeing operable when positioned in the dermal layer rather than in ablood vessel, but retain or improve upon the accuracy of a blood vesselsensor. For example, many of these embodiments do not exhibit the extentof physiological lag that is experienced by sensors positioned in thesubcutaneous space.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 schematically illustrates alternative sensor applicator setconfigurations. In Panel A, the longest axis of the insertion needle isdisposed substantially parallel to the longest axis of the sensor. InPanel B, which schematically illustrates a sensor applicator setaccording to one embodiment of the present disclosure, the longest axisof the insertion needle is disposed at an angle relative to the longestaxis of the sensor.

FIG. 2 shows the formation of a sensor in Panels A-D that include aworking electrode according to one embodiment of the present disclosure.

FIG. 3 schematically illustrates a sensor in Panels A-C according to oneembodiment of the present disclosure.

FIG. 4 schematically illustrates a sensor applicator set in Panels A-Caccording to one embodiment of the present disclosure.

FIG. 5 schematically illustrates a sensor in Panels A-C according to oneembodiment of the present disclosure.

FIG. 6 schematically illustrates a sensor applicator set in Panels A-Caccording to one embodiment of the present disclosure.

FIG. 7 provides, in Panels A-B, glucose concentration data obtainedusing a dermal glucose sensor according to one embodiment of the presentdisclosure, compared to data obtained using a subcutaneous glucosesensor. Measured current from the dermal sensor (DS) shown on the leftaxis of the graphs and the measured current from the subcutaneous sensor(SC) on the right axis of the graphs.

DETAILED DESCRIPTION

Before the sensor applicator sets and methods of the present disclosureare described in greater detail, it is to be understood that theapplicator sets and methods are not limited to particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the applicator sets and methods will be limited only by theappended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the applicator sets and methods. Theupper and lower limits of these smaller ranges may independently beincluded in the smaller ranges and are also encompassed within theapplicator sets and methods, subject to any specifically excluded limitin the stated range. Where the stated range includes one or both of thelimits, ranges excluding either or both of those included limits arealso included in the applicator sets and methods.

Certain ranges are presented herein with numerical values being precededby the term “about.” The term “about” is used herein to provide literalsupport for the exact number that it precedes, as well as a number thatis near to or approximately the number that the term precedes. Indetermining whether a number is near to or approximately a specificallyrecited number, the near or approximating unrecited number may be anumber which, in the context in which it is presented, provides thesubstantial equivalent of the specifically recited number.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the applicator sets and methods belong. Although anyapplicator sets and methods similar or equivalent to those describedherein can also be used in the practice or testing of the applicatorsets and methods, representative illustrative applicator sets, methodsand materials are now described.

All publications and patents cited in this specification are hereinincorporated by reference as if each individual publication or patentwere specifically and individually indicated to be incorporated byreference and are incorporated herein by reference to disclose anddescribe the applicator sets, methods and/or materials in connectionwith which the publications are cited. The citation of any publicationis for its disclosure prior to the filing date and should not beconstrued as an admission that the present applicator sets and methodsare not entitled to antedate such publication by virtue of priorinvention. Further, the dates of publication provided may be differentfrom the actual publication dates which may need to be independentlyconfirmed.

It is noted that, as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation.

It is appreciated that certain features of the applicator sets andmethods, which are, for clarity, described in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the applicator sets and methods, whichare, for brevity, described in the context of a single embodiment, mayalso be provided separately or in any suitable sub-combination. Allcombinations of the embodiments are specifically embraced by the presentinvention and are disclosed herein just as if each and every combinationwas individually and explicitly disclosed, to the extent that suchcombinations embrace operable processes and/or devices/systems/kits. Inaddition, all sub-combinations listed in the embodiments describing suchvariables are also specifically embraced by the present applicator setsand methods and are disclosed herein just as if each and every suchsub-combination was individually and explicitly disclosed herein.

As will be apparent to those of skill in the art upon reading thisdisclosure, each of the individual embodiments described and illustratedherein has discrete components and features which may be readilyseparated from or combined with the features of any of the other severalembodiments without departing from the scope or spirit of the presentapplicator sets and methods. Any recited method can be carried out inthe order of events recited or in any other order which is logicallypossible.

In further describing embodiments of the present disclosure, aspects ofembodiments of the subject applicator sets will be described first ingreater detail. Thereafter, aspects of embodiments of the methods ofusing the applicator sets are described in greater detail.

Sensor Applicator Sets

An issue with conventional in vivo analyte monitoring systems designedto determine analyte concentration in interstitial fluid (ISF) of thesubcutaneous space is that there is a substantial time lag that existsbetween the ISF analyte concentration and the blood analyteconcentration. This is the case when the monitored analyte is glucose,and for other analytes whose concentration changes quickly. (Glucosewill be used primarily as an exemplary analyte herein, but it is to beunderstood that other analytes may be monitored.) For example, a timelag in the distribution of glucose from blood to the interstitium hasbeen observed. As a result of this lag, ISF glucose concentrations donot correlate exactly with blood glucose concentrations at a given pointin time. The present inventors have surprisingly discovered that—ascompared to traditional in vivo analyte monitoring systems whichdetermine ISF analyte concentrations in subcutaneous tissue (e.g., 3 mmto 10 mm beneath the surface of the skin)—in vivo monitoring of dermalfluid (e.g., 0.5 mm to 3 mm) analyte concentration provides analyteconcentration data with markedly reduced lag times as compared to bloodanalyte concentration (e.g., venous glucose). Accordingly, analyteconcentration data obtained using a dermal analyte sensor correlatesmore closely to the analyte concentration in blood as compared to invivo ISF sensors.

Despite the above-mentioned discovery of the advantages afforded bymeasuring analyte concentrations in dermal fluid, significant technicalhurdles exist with respect to the insertion of one or more sensorcomponents, e.g., a working electrode, into and no deeper than a dermallayer of a subject. For example, the significantly reduced scale of thesensor component(s) necessary for a dermal sensor as compared to anISF/subcutaneous sensor renders the dermal sensing components extremelyfragile and therefore more susceptible to breaking under the modestforces exerted on the sensor by the skin surface and/or underlyingtissue as the sensor is being inserted.

As such, monitoring the concentration of an analyte in the dermal layerof a subject requires more than simply scaling down the size of anISF/subcutaneous analyte sensor. New strategies for inserting componentsof a dermal analyte sensor are needed, and are therefore provided in thepresent disclosure. Technical challenges of sensors sized for dermalsensing are also significant. For example, sensors must be sized so thatthey are only positionable in the dermal layer, but must also be able toprovide acceptable current densities, stabilities, and sensitivities, inaddition to being manufacturable with any consistency and reliability,e.g., by high speed manufacturing techniques. These challenges are metby the devices and methods of the present disclosure.

The present disclosure provides various embodiments of dermal sensors,sensor applicator sets, and methods of using and making the same.Detecting the presence and/or concentration of a dermally-positionedsensor is also provided, where the detection step is carried out usingan electrochemical measurement technique. For example, a dermal sensormay detect current or may employ potentiometry. According to certainembodiments, an analyte-associated signal obtained from adermally-positioned sensor is detected by an electrochemical measurementtechnique including, but not limited to, amperometry, coulometry,voltammetry, and potentiometry. Dermal sensors may also provide analyteinformation using optical or colorimetric means.

A sensor applicator set is a collection of elements including a dermalin vivo analyte sensor readied for dermal positioning (at least asensing region of a working electrode), and an insertion needle thatpositions the dermal sensor only in the dermal layer of a subject. Othersensor electrodes may be included for dermal positioning or may bepositioned remotely from the dermal area in which the working electrodeis positioned, e.g., may be positioned outside a subject's body. Forexample, other than a working electrode and particularly a sensingregion of a working electrode, additional sensor components may beincluded such as one or a second working electrode, a counter electrode,reference electrode, or a counter/reference electrode. The presentdisclosure of inserting a dermal sensor in a dermal space contemplatesall of these various embodiments unless specifically noted and at leastincludes dermally positioning at least a sensing region of a workingelectrode of a sensor. The in vivo analyte sensors designed specificallyfor dermal positioning are referred to herein as a sensor, dermalsensor, analyte sensor, in vivo sensor, and the like.

As will be described below, the embodiments disclosed herein can also beconfigured and used such that the sensor and/or insertion needle extendbeyond the dermal layer and into the subcutaneous layer. The presentdisclosure of inserting a sensor into or through subcutaneous tissuecontemplates all variations of electrode positioning unless specificallynoted and at least includes positioning at least a sensing region of aworking electrode of a sensor into the subcutaneous tissue. Additionalsensor components may be included such as one or a second workingelectrode, a counter electrode, reference electrode, or acounter/reference electrode, and each of these may be positioned in thesubcutaneous tissue, the dermal tissue, or any combination thereof, whenthe sensing region of the working electrode is in either the dermallayer or the subcutaneous layer.

In addition to a dermal sensor and sensor insertion needle, thecollection of sensor applicator elements optionally includes one or moreelements for mounting and/or fixing the sensor and insertion needle at adesired distance and/or orientation (e.g., angle) relative to areference point such as each other before, during, or after the sensingregion of the working electrode is inserted at the dermal layer. Otheroptional elements, such as elements that facilitate manually driven ornon-manually driven (e.g., automatically) or semi-manually driveninsertion of the sensor and/or insertion needle may be included. Thesubject sensor applicator sets may include elements in addition to thedermal sensor and insertion needle that insert a sensing portion of aworking electrode in a dermal area, as well as removing one or moreelements (e.g., the insertion needle) of the applicator set before,during, or after the sensing region of the working electrode is insertedat the dermal layer.

The dermal insertion needle is configured to create an insertion path ata skin site of a subject to place a sensor in the dermal layer and nofurther. The dermal sensor is inserted into the insertion path and atthe dermal layer, but not through a dermal layer. In certain aspects,during operation of the applicator set, the insertion needle creates aninsertion path for the sensor before the insertion of the sensor into,but not through, a dermal layer is initiated. In other words, aninsertion sequence in an embodiment includes inserting the insertionneedle to the dermal layer to first form a path into the dermal layer,and then inserting a dermal sensor in the formed path to and into thedermal layer, where advancing the dermal sensor in the formed path mayoccur before the insertion needle is removed from the formed path orafter the insertion needle is removed. For example, an insertion needlemay be inserted (e.g., manually or automatically) at a skin site to adesired dermal depth to create a suitable insertion path for the sensorin the dermal layer. Upon removal of the insertion needle from thedermal layer, the sensor is then inserted (e.g., manually orautomatically using mechanical components) into the insertion path, butnot through a dermal layer at the skin site of the subject.

In other aspects, during operation of the applicator set, the insertionneedle creates an insertion path for the sensor as the sensor is beinginserted into but not through a dermal layer at the skin site of thesubject. That is, the insertion needle and the sensor move together andare simultaneously inserted into the skin of the subject, where theinsertion needle and sensor are in an orientation relative to each othersuch that the insertion needle creates an insertion path through whichthe sensor travels as the insertion needle and sensor pass through theskin surface together and to a desired dermal depth. A dermal sensor mayfollow, but trail, an insertion needle through a needle-formed insertionpath to the dermal layer.

Due to the small scale of the dermal sensors and the need for creating asimilarly small scaled insertion path for the sensor in the dermallayer, the conventional methodology of positioning the sensor within alumen of an insertion needle is not possible. In particular, positioningof the sensor within the lumen of the needle requires that the needle issufficiently large to house the sensor resulting in a needle having arelatively larger diameter than the sensor thereby creating a widerinsertion path than the width of the dermal sensor. Since the dermalsensor is to be positioned in the dermal layer of the skin, having aninsertion path that is significantly wider than the width of than thesensor increases the possibility of instability of the positionedsensor, irritation at the insertion site, damage to surrounding tissue,and breakage of capillary blood vessels resulting in fouling of thedermal fluid with blood.

Likewise, positioning a dermal sensor in an adjacent side-by-sidearrangement with its insertion needle also creates an undesirableresult, including an insertion path that is too wide. This arrangementcreates an insertion path at the surface of the skin that is adjacentto—and different from—the location at which the sensor would come intocontact with the surface of the skin. The disadvantage of thisarrangement in which the needle and sensor are parallel to each otherand are both at a normal angle relative to the skin is exemplified inPanel A of FIG. 1. In particular, Panel A of FIG. 1 shows sensorapplicator set 100 that includes base 101 that holds dermal sensor 102and insertion dermal insertion needle 104. Proximal region 106 of sensor102 and proximal region 108 of insertion needle 104 are next to eachother and are in parallel orientation with respect to each other, i.e.,are not converging towards each other. Sensor 102 and needle 104 alsoinclude distal regions 107 and 109, respectively. Proximal and distalare relative terms defined by a spatial relationship between elements incomparison to the point of reference of the base of an applicator setsuch that sensor proximal region 106 is closer to base 101 than sensordistal region 107. The longest axis Ln of insertion needle 104 isdisposed parallel to the longest axis Ls of sensor 102, and as shown areparallel to each other and do not converge towards each other. In thisparallel and non-converging orientation, inserting the applicator setinto the subject results in the application of forces at two differentlocations on the skin surface—indicated by lines 103 and 105 at thesensor distal region 107 and the insertion needle distal region 109.Therefore, this system would not allow for co-localizing the point atwhich the insertion needle 104 and sensor 102 contact the surface of theskin. In fact, it provides for two different contact points 103 and 105as exemplified in Panel A of FIG. 1.

In contrast, the present inventors have discovered that by angling thesensor and/or insertion needle relative to a reference point enablesco-localization of the tip of the insertion needle and the tip of thesensor and creates a single contact point at the surface of the skin. Assuch, the insertion needle creates a leading edge at the surface of theskin to form an insertion path into the dermal layer for the sensor asthe sensor is inserted into a subject. The insertion needle and/ordermal sensor may be angled relative to a reference point (e.g., eachother, surface of the skin, or the base of the applicator set) forinsertion, where the angle of the needle differs from the angle of thesensor. For example, the reference point may be the skin surface to bebreached for dermal insertion, or may be a reference or component of thesensor applicator set. In some embodiments, the needle may be disposedat an angle relative to the sensor. For example, when designed so thatthat the needle is angled relative to the sensor, the needle creates aleading edge for the sensor during operation of the applicator set.

This discovery is schematically illustrated in FIG. 1, panel B. Anapplicator set according to embodiments of the present disclosure isschematically illustrated in FIG. 1, Panel B. In these embodiments, thesensor and/or needle are angled relative to a reference point. Forexample, one of the sensor or insertion needle may be angled relative tothe other, or one or both may be angled relative to a skin surface oranother element of the applicator set. The angles of each may differ andthe needle may be angled a first angle and the sensor may be angled asecond angle. As shown in FIG. 1, panel B, applicator set 110 includesbase 111 that holds sensor 112 and insertion needle 114 in anorientation so that they are not spaced apart a uniform distance fromeach other, but rather have a varying, i.e., changing, distance betweenthem so that needle 114 converges towards sensor 112 to come close to,and in certain embodiments physically contacts, sensor 112. Sensorproximal region 116 and needle proximal region 118 are spaced apart attheir proximal regions, but are close to each other or are in contactwith each other at converging region C to provide an angle 120 betweenthe sensor and needle. Angle 120 can range from 5° to 20°, where in someembodiments angle 120 ranges from 5° to 17° or 7° to 15° or 9° to 13°,e.g., 9°, 10°, 11°, 12°, or 13°.

The longest axis Ln₁ of insertion needle 114 and the longest axis Ls₁converge towards each other. In converging region C, the insertionneedle and the dermal sensor come close to or contact each other atlocations distal to proximal portions 116 and 118, respectively. In thisparticular example shown in FIG. 1, panel B, the insertion needle islonger than the dermal sensor, and a non-terminal (or “body”) portion(i.e., an intermediate region 121) of the insertion needle comes closeto (the terminal end of the convergence) or contacts the dermal sensorat the sensor distal end 117, but not at the sensor proximal end whichremains spaced apart from the needle. However, variations are possible,e.g., such as selecting a length and/or angle of the insertion needlesuch that the needle and sensor come close to each other, and in someembodiments, contact each other at or near the distal ends of both theneedle and sensor.

In any event, as a result of the insertion needle being disposed atangle 120 relative to the dermal sensor, and upon insertion of theneedle and sensor into a subject, the insertion needle creates aninsertion path for the sensor such that forces acting upon the dermalsensor from a tissue surface or underlying tissue of the subject duringinsertion are eliminated or reduced as compared to the forces actingupon a sensor in the applicator set configuration shown in FIG. 1, PanelA. That is, when the insertion needle is angled relative to the dermalsensor to contact (or come close to contacting) the sensor at a portionof the dermal sensor (e.g., at or near the distal end of the sensor), itis not required that the sensor form its own insertion path through thetissue surface and/or underlying tissue of the subject. Rather, theforces applied by the tissue surface or underlying tissue duringinsertion are primarily applied to and absorbed by the insertionneedle—indicated by line 115 at the tip of insertion needle 114. Inaddition, by contacting the dermal sensor in the embodiments in whichthe needle physically contacts the sensor, the insertion needle can alsoassist in stabilizing the sensor by counteracting forces applied by thetissue of the subject to the sensor in the direction of the insertionneedle. In this way, the portion of the dermal sensor inserted into thedermal layer (i.e., the insertion length or sensing portion of thesensor) can have a length of 0.5 mm to 3 mm, or even 1 mm to 2 mm, andcan be inserted through the skin and into (and not through) a dermallayer of a subject and used to determine analyte levels of a dermalfluid without damage to the sensor.

An insertion needle may be disposed at an angle relative to theapplicator base such that the needle is not at a 90° right anglerelative to the base, but that it is positioned at an acute angle (e.g.,1° to 89°) relative to the base and angled in the direction towards thedermal sensor of the base, as exemplified in FIG. 1, panel B. Forexample, the angle of the needle 114 can also be described by therelationship of the needle to the base 111 to which it is held. Panel Bof FIG. 1 shows angle 122 between axis Ln₁ of needle 110 and base 111.Angle 122 is an acute angle resulting in angling the distal end of theneedle in the direction of the sensor. Angle 122 can range from 65° to85°, including 70°, 75°, or 80°.

The angle of a sensor can also be described by the relationship pf thesensor to the base 11 to which it is held. As shown in FIG. 1 Panel B,axis Ls₁ of the dermal sensor is disposed at angle 123 relative to thebase, where in this embodiment angle 123 is a perpendicular angle (i.e.,90°) between the sensor and the base, and the sensor is therefore alsoat a 90° angle relative to the skin surface into which it is inserted ifinserted with axis Ls₁ normal to the skin. Accordingly, as shown inpanel B of FIG. 1, embodiments include longitudinal axis Ln₁ of theinsertion needle disposed at an acute angle 122 relative to the base andaxis Ln₁ and the longest axis of the sensor Ls₁ converge towards eachother at area C. While angle 123 is shown in Panel B as a 90° angle, itcan be anywhere from 80°-100°.

In certain embodiments, a needle and sensor are parallel to each otherand both are at a non-normal angle relative to the skin.

The insertion needle is dimensioned such that the applicator setprovides for insertion of at least a portion of the dermal sensor intothe dermal layer, but not through the dermal layer of the skin.According to certain embodiments, the insertion needle has a crosssectional diameter (width) of from 0.1 mm to 0.5 mm. For example, theinsertion needle may have a diameter of from 0.1 mm to 0.3 mm, such asfrom 0.15 mm to 0.25 mm e.g., 0.16 mm to 0.22 mm in diameter. A givenneedle may have a constant, i.e., uniform, width along its entirelength, or may have a varying, i.e., changing, width along at least aportion of its length, such as the tip portion used to pierce thesurface of the skin.

An insertion needle has a length to insert a dermal sensor just into thedermal layer, and no more. Insertion depth may be controlled by thelength of the needle and/or configuration of the base other applicatorcomponents that limit insertion depth.

An insertion needle may have a length of from 1.5 mm to 25 mm. Forexample, the insertion needle may have a length of from 1 mm to 3 mm,from 3 mm to 5 mm, from 5 mm to 7 mm, from 7 mm to 9 mm, from 9 mm to 11mm, from 11 mm to 13 mm, from 13 mm to 15 mm, from 15 mm to 17 mm, from17 mm to 19 mm, from 19 mm to 21 mm, from 21 mm to 23 mm, from 23 mm to25 mm, or a length greater than 25 mm. It will be appreciated that whilean insertion needle may have a length up to 25 mm, in certainembodiments the full length of the needle is not inserted into thesubject because it would extend beyond the dermal space. Non insertedneedle length may provide for handling and manipulation of the needle inan applicator set. Therefore, while an insertion needle may have alength up to 25 mm, the insertion depth of the needle in the skin on asubject in those certain embodiments will be limited to the dermallayer, e.g., about 1.5 mm to 4 mm, depending on the skin location, asdescribed in greater detail below. However, in all of the embodimentsdisclosed herein, the insertion needle can be configured to extendbeyond the dermal space, such as into (or even fully through)subcutaneous tissue (e.g., 3 mm to 10 mm beneath the surface of the skindepending on the location of the skin on the body). Any of the insertionneedles described herein may be solid insertion needles, where by“solid” is meant that the needles do not have an internal space and/orlumen (e.g., are not hollow), or they may include an internal space orlumen. An insertion needle of the subject applicator sets may be bladedor non-bladed.

Likewise, in certain embodiments, a dermal sensor is sized so that atleast a portion of the sensor is positioned in the dermal layer and nomore, and a portion extends outside the skin in the transcutaneouslypositioned embodiments. That is, a dermal sensor is dimensioned suchthat when the dermal sensor is entirely or substantially entirelyinserted into the dermal layer, the distal-most portion of the sensor(the insertion portion or insertion length) is positioned within thedermis of the subject and no portion of the sensor is inserted beyond adermal layer of the subject when the sensor is operably dermallypositioned.

The dimensions (e.g., the length) of the sensor may be selectedaccording to the body site of the subject in which the sensor is to beinserted, as the depth and thickness of the epidermis and dermis exhibita degree of variability depending on skin location. For example, theepidermis is only about 0.05 mm thick on the eyelids, but about 1.5 mmthick on the palms and the soles of the feet. The dermis is the thickestof the three layers of skin and ranges from about 1.5 mm to 4 mm thick,depending on the skin location. For implantation of the distal end ofthe sensor into, but not through, the dermal layer of the subject, thelength of the inserted portion of the dermal sensor should be greaterthan the thickness of the epidermis, but should not exceed the combinedthickness of the epidermis and dermis. Methods may include determiningan insertion site on a body of a user and determining the depth of thedermal layer at the site, and selecting the appropriately-sizedapplicator set for the site.

In certain aspects, the sensor is an elongate sensor having a longestdimension (or “length”) of from 0.25 mm to 4 mm. The length of thesensor that is inserted, in the embodiments in which only a portion of asensor is dermally inserted, ranges from 0.5 mm to 3 mm, such as from 1mm to 2 mm, e.g., 1.5 mm. The dimensions of the sensor may also beexpressed in terms of its aspect ratio. In certain embodiments, a dermalsensor has an aspect ratio of length to width (diameter) of about 30:1to about 6:1. For example, the aspect ratio may be from about 25:1 toabout 10:1, including 20:1 and 15:1. The inserted portion of a dermalsensor has sensing chemistry.

However, all of the embodiments disclosed herein can be configured suchthat at least a portion of the sensor is positioned beyond the dermallayer, such as into (or through) the subcutaneous tissue (or fat). Forexample, the sensor can be dimensioned such that when the sensor isentirely or substantially entirely inserted into the body, thedistal-most portion of the sensor (the insertion portion or insertionlength) is positioned within the subcutaneous tissue (beyond the dermisof the subject) and no portion of the sensor is inserted beyond thesubcutaneous tissue of the subject when the sensor is operablypositioned. As mentioned, the subcutaneous tissue is typically presentin the region that is 3 mm to 10 mm beneath the outer skin surface,depending on the location of the skin on the body.

For implantation of the distal end of the sensor into, but not through,the subcutaneous tissue of the subject, the length of the insertedportion of the sensor should be greater than the thickness of theepidermis and dermis, but should not exceed the combined thickness ofthe epidermis, dermis, and subcutaneous tissue (when inserted at anormal angle to the skin surface—a non-normal angle allows an insertionportion of the sensor that can exceed these combined thicknesses sincethe absolute depth of penetration is less than the length of theinserted portion of the sensor). For example, the length of the sensorthat is inserted can be greater than 3 mm, or any length that places thesensing region of the working electrode into the subcutaneous tissue,further taking into account insertion of the sensor at a non-normalangle to the skin surface (e.g., 70 degrees), which will require alonger sensor. In all embodiments, the sensor can be configured toextend beyond the subcutaneous tissue as well.

The subject applicator sets may include a sensor having one or morestructural features that enhance the association of the sensor with theinsertion needle and/or facilitates the disposition of the insertionneedle at the desired angle relative to the sensor. In certain aspects,a distal end of the sensor includes a groove that is complementary(e.g., in a male-female-type relationship) to the exterior shape anddimensions of the insertion needle (or vice versa). The groove may havea shape and dimension complementary to an exterior area of the insertionneedle (see, e.g., grooves 411 and 611 in FIG. 4, Panel A and FIG. 6,Panel A, respectively) such as a distal end portion of the insertionneedle. In embodiments where the sensor has a groove having a shapecomplementary to the insertion needle, the groove may have an angle thatcorresponds to the angle of the insertion needle (e.g., angle 120 ofFIG. 1, panel B). In this way, the insertion needle may be supported orstabilized at the desired angle by the grooved portion of the sensor. Inother aspects, the distal end of the sensor does not have a groovecomplementary to the insertion needle, but rather has an angle (e.g., aflat, angled surface) that corresponds to the desired angle of theinsertion needle. The angled portion of the distal end of the sensor mayperform the same or similar function as the aforementioned groove, inthat the insertion needle may be supported or stabilized at the desiredangle by the angled portion at the distal end of the sensor.

According to certain embodiments, the subject devices and applicatorsets include a sensor that is a microprojection having a solidmicroneedle-like structure without a central bore (or lumen) throughwhich liquid is injected or withdrawn. Suitable microprojections may beobtained, e.g., by singulating individual microprojections from aplurality of microprojections present on a roll or other sensor uponwhich a plurality of microprojections is disposed.

Sensors of the subject applicator sets may be made of a conductivematerial and an insulative material that is nonconductive,semiconductive, or conductive. In certain embodiments, the sensor ismade of a nonconductive or conductive plastic. For example, the sensormay be a nonconductive plastic microprojection upon which one or morelayers of conductive material are disposed (e.g., one, two, or moreconductive layers may be disposed on the plastic microprojection). Theone or more layers of conductive material may serve as the workingelectrode. Additional layers may be disposed on the one or moreconductive layers, such as a sensing layer (e.g., a layer that includesan analyte-responsive enzyme, and may also include a redox mediator, orboth), a mass transport limiting layer that limits access of certainchemical species (e.g., the analyte, an interfering component, or thelike) to a sensing layer, and/or any other layer that may improve theperformance or provide additional desired functionalities to the sensor.

The formation of a sensor that includes a working electrode according toone embodiment of the present disclosure is shown in FIG. 2. Panel A isan uncoated sensor, which in this example is a plastic microprojection202 having a length of about 1.5 mm. The plastic microprojection may becoated (e.g., sputter coated) with a layer of conductive material (inthis example, gold layer 204) to form a working electrode as shown inPanel B. The coated sensor may be further coated with an optional layerof a second material (in this example, carbon layer 206) as shown inPanel C. This second layer may be useful, e.g., to enhance electrodeconductivity and/or adhesion of any additional layers (e.g., a sensinglayer) to the electrode. In the embodiment of FIG. 2, the electrodeincludes sensing layer 208 that includes an analyte-responsive enzymedisposed on the second layer, as shown in Panel D. A redox mediator mayalso be included with the enzyme. Included as an outermost layer (notshown) in the embodiment of FIG. 2 is an analyte transport limitinglayer.

A sensor of the subject applicator sets may be made of a conductivematerial which may exhibit sufficient conductivity to obviate any needfor an additional conductive coating to provide a working electrodecapable of electrochemical determination of the concentration of theanalyte. According to certain aspects, the conductive material is aconductive plastic. The conductive plastic may include a polymer matrix(e.g., a non-conductive or substantially non-conductive polymer matrix)that includes a conductive material interspersed therein. The polymermatrix may include any polymer suitable for forming a conductiveplastic, including but not limited to, a polyether block amide polymer.The conductive material may be a conductive material that conferssufficient conductivity to the polymer matrix. Such materials mayinclude conductive particulate matter, such as conductive metalparticles, microspheres coated with a conductive material, carbon,and/or the like. In certain aspects, the conductive materialinterspersed in the polymer matrix is carbon. When the conductivematerial interspersed within the polymer matrix is carbon, the carbonmay be present in the polymer matrix in an amount ranging from 5% to 30%w/w. For example, the carbon may be present in the polymer matrix in anamount ranging from 7% to 20% w/w, such as from 8% to 12% w/w, e.g., 10%w/w.

A sensor that can be used in an applicator set according to oneembodiment of the present disclosure is schematically illustrated inFIG. 3. As shown in Panel A, the sensor includes substrate 302 havinggroove 304, with the sensor positioned on base 306. In this example, thesubstrate and base are made of plastic. To form a working electrode, allor a portion of the substrate (and optionally one or more surfaces ofthe base) is coated with a conductive layer (e.g., Au layer 308) bysputter coating or any other suitable approach for providing aconductive layer on a plastic substrate (Panel B). Additional layers maybe applied to the substrate and/or base, such as carbon layer 310disposed on the Au-coated substrate (e.g., by dip coating, spraying orsubmersion), as shown in Panel C. A sensing layer, a protective and/ormass transport limiting layer, and/or the like may further be providedon carbon layer 310 to enhance the performance of and/or provideadditional functionalities to the sensor.

Various components of a disassembled sensor applicator set 416 accordingto one embodiment of the present disclosure are shown in FIG. 4, PanelA. The proximal end of insertion needle 402 is disposed within or onmolded hub 404. Insertion needle 402 is disposed at an angle 403 (suchas between 9° and 13°, e.g., 11°) relative to vertical axis 405extending from the top surface of molded hub 404, and/or angle 415 mayalso be formed similar to angle 122 of Panel B of FIG. 1. According tothis embodiment, the applicator set includes dermal sensor 406 having anappropriate size, shape, and dimension for insertion into a dermal layerof a subject and for generating analyte-responsive signals in responseto analyte present in the dermal fluid. Sensor 406 may be the same as,similar to, or different from the sensor shown in FIG. 3, Panel C. Wire408 is connected to a conductive coating on the base 407 of sensor 406and facilitates electrical communication between sensor 406 andcomponents of an analyte sensing system, e.g., a voltage source, controlelectronics, and/or the like. View 410 is a magnified view of sensor 406and wire 408 connected thereto. As can be seen in view 410, dermalsensor 406 includes groove 411 having a shape and angle complementary toa portion of insertion needle 402. In this embodiment, the applicatorset includes assembly mount 412 for mounting/fixing the sensor andinsertion needle in the desired position relative to each other, as wellas adhesive 414 for securing the dermal sensor in its final positionupon insertion into the subject.

Assembled sensor applicator set 416, which includes dermal sensor 406and insertion needle 402 disposed at an angle relative to sensor 406, isshown in FIG. 4, Panel B (left). Adhesive 414 is cut-away to show theother elements of applicator set 416, and a magnified view of the sensorand insertion needle associated with each other via their complementaryshapes is also shown in FIG. 4, Panel B. A side view of assembledapplicator set 416 is provided in FIG. 4, Panel C, including a magnifiedside view of dermal sensor 406 and insertion needle 402 on the right.

As described above, according to certain embodiments, applicator sets ofthe present disclosure may include a dermal sensor molded (e.g., byinjection molding) from a nonconductive or conductive plastic. Anexemplary applicator set 502 according to this embodiment is shown inFIG. 5. Dermal sensor 501 and base 503, e.g., molded from conductiveplastic, is shown in FIG. 5, Panel A. The conductive plastic may includea polymer matrix (e.g., a polyether block amide polymer) having aconductive material (e.g., carbon particles) disposed therein, asdescribed hereinabove. In certain aspects, a distal portion of thesensor 501 includes a divot. An exemplary divot 504 is shown in FIG. 5,Panel B. When a dermal sensor includes divot or through hole, sensingreagents or the like may be deposited therein. If the divot is to beused for deposition of sensing reagents therein, the area and/or volumeof the divot may be selected during the manufacturing design process toprovide one or more desired sensor characteristics (e.g., workingelectrode characteristics), such as a particular sensitivity in responseto the analyte, e.g., where the sensitivity (e.g., analyte- responsivesignal) may be increased or decreased by increasing or decreasing thearea and/or volume of the recess, respectively. A dermal sensor maytherefore include one or more structural features (e.g., a molded divotfor deposition of sensor reagents, a molded groove having a shapecomplementary to the insertion needle, and/or the like) at one or moreregions of the sensor. Electrical connecting wire 506 connected to theconductive plastic of the base is shown in FIG. 5, Panel C. The wire maybe employed to facilitate electrical communication between sensor andbase 502 and components of an analyte sensing system, e.g., a voltagesource, control electronics, and/or the like.

Components of a disassembled sensor applicator set 616 according to oneembodiment of the present disclosure are shown in FIG. 6, Panel A. Theproximal end of insertion needle 602 is disposed within or on hub 604.Insertion needle 602 is disposed at an angle 603 (such as between 9° and13°, e.g., 11°) relative to vertical axis 605 extending from the topsurface of molded hub 604, which may be its angle relative to the sensorupon assembly of the applicator set, and/or angle 615 may also be formedsimilar to angle 122 of Panel B of FIG. 1. According to this embodiment,the applicator set includes molded dermal sensor 606 and base 607configured (e.g., sized, etc.) for insertion into a dermal layer of asubject and for generating analyte-responsive signals in response toanalyte present in the dermal fluid. Molded dermal sensor 606 may be thesame as, similar to, or different from the molded sensor shown in FIG.5. Electrical connecting wire 608 is connected to the base 607 of moldedsensor 606 and facilitates electrical communication between moldedsensor 606 and components of an analyte sensing system, e.g., a voltagesource, control electronics, and/or the like. View 610 is a magnifiedview of molded dermal sensor 606 and wire 608 connected thereto. As canbest be seen in view 610, molded dermal sensor 606 includes a groove 611having a shape and angle complementary to a body portion of insertionneedle 602. In this embodiment, the applicator set includes assemblymount 612 for mounting/fixing the sensor and insertion needle in thedesired position relative to each other, as well as adhesive 614 forsecuring the sensor in its final position upon insertion into thesubject.

Assembled sensor applicator set 616, which includes dermal sensor 606and insertion needle 602 disposed at an angle relative to sensor 606, isshown in FIG. 6, Panel B (left). Adhesive 614 is cut-away in FIG. 6,Panel B to show the other elements of applicator set 616. A magnifiedview of the dermal sensor and the insertion needle associated with eachother via their complementary shapes is shown in FIG. 6, Panel B(right). A side view of assembled applicator set 616 is provided in FIG.6, Panel C (left), including a magnified view of dermal sensor 606 andinsertion needle 602 on the right.

Exemplary features and components of the sensors employed in the subjectdevices, applicator sets and methods are described in greater detailbelow. Any of the sensors and sensor applicator sets described above mayinclude any such features and components, alone or in combination.

Conductive Material

As set forth above, in certain aspects, a dermal sensor employed by asubject applicator set is a dermal sensor that includes one or moreconductive materials, e.g., in the form of conductive layers, integratedparticles, and the like. The one or more conductive materials conferconductivity to the sensor, e.g., when the sensor includes anon-conductive or substantially non-conductive material (e.g., anon-conductive plastic material). For example, a conductive layerdisposed on a non-conductive material may constitute the workingelectrode of the sensor. In certain aspects, a second conductivematerial, e.g., a conductive layer, electrically isolated from the firstconductive material or layer, e.g., by an electrically insulating layer,may be added to provide a second electrode in addition to the workingelectrode (e.g., a counter or counter/reference electrode, a referenceelectrode, or the like).

A dermal sensor described herein may include one or more conductivelayers made of a material independently selected from gold, carbon,platinum, ruthenium, palladium, silver, silver chloride, silver bromide,and combinations thereof. A conductive layer may be a layer of gold, tinoxide, platinum, ruthenium dioxide or palladium, indium tin oxide, zincoxide, fluorine doped tin oxide, as well as other non-corrodingmaterials known to those skilled in the art. The conductive layer can bea combination of two or more conductive materials. For example, theconductive layer may be constructed from a layer of gold on a firstregion of the sensor and a layer of carbon on a second region of thesensor.

The conductive layer may be applied to the sensor or a layer thereof bybeing deposited, such as by vapor deposition or vacuum deposition orotherwise sputtered, printed on a flat surface or in an embossed orotherwise recessed surface, transferred from a separate carrier orliner, etched, or molded. Suitable methods of printing includescreen-printing, piezoelectric printing, ink jet printing, laserprinting, photolithography, painting, gravure roll printing, transferprinting, and other known printing methods.

Sensing Layer

At least one or more working electrodes of a dermal sensor may include asensing layer that includes sensing reagents to facilitate determinationof a concentration of an analyte of interest. The sensing layer includesone or more components designed to facilitate the electrolysis of theanalyte. The sensing layer may include, for example, an analyteresponsive enzyme to catalyze a reaction of the analyte and produce aresponse at the working electrode, an electron transfer agent toindirectly or directly transfer electrons between the analyte and theworking electrode, or both.

A variety of different sensing layer configurations may be used. Incertain embodiments, the sensing layer is deposited on the conductivematerial of a working electrode. The sensing layer may extend beyond theconductive material of the working electrode. In some cases, the sensinglayer may also extend over other electrodes, e.g., over a counterelectrode and/or reference electrode (or counter/reference electrode).The sensing layer may be integral with the material of an electrode.

For example, a sensor for sensing glucose may include a first sensinglayer which is spaced apart from the working electrode and contains aglucose-responsive enzyme, for example, glucose oxidase or glucosedehydrogenase. The reaction of glucose the presence of the appropriateenzyme forms hydrogen peroxide. A second sensing layer may be provideddirectly on the working electrode and contains a peroxidase enzyme andan electron transfer agent to generate a signal at the electrode inresponse to the hydrogen peroxide. The level of hydrogen peroxideindicated by the sensor then correlates to the level of glucose.

Another sensor which operates similarly can be made using a singlesensing layer with both the glucose and the peroxidase being depositedin the single sensing layer.

A sensing layer that is in direct contact with the working electrode maycontain an electron transfer agent to transfer electrons directly orindirectly between the analyte and the working electrode, and/or anenzyme to facilitate a reaction of the analyte. For example, a glucose,or oxygen electrode may be formed having a sensing layer which containsan enzyme, such as glucose oxidase, and an electron transfer agent thatfacilitates the electro-oxidation of the glucose.

In other embodiments, the sensing layer is not deposited directly on theworking electrode. Instead, the sensing layer may be spaced apart fromthe working electrode, and separated from the working electrode, e.g.,by a separation layer. A separation layer may include one or moremembranes or films or a physical distance. In addition to separating theworking electrode from the sensing layer the separation layer may alsoact as a mass transport limiting layer and/or an interferent eliminatinglayer and/or a biocompatible layer.

In certain embodiments which include more than one working electrode,one or more of the working electrodes do not have a correspondingsensing layer, or have a sensing layer which does not contain one ormore components (e.g., an electron transfer agent and/or enzyme) neededto electrolyze the analyte. Thus, the signal at this working electrodecorresponds to background signal which may be removed from the analytesignal obtained from one or more other working electrodes that areassociated with fully-functional sensing layers by, for example,subtracting the signal.

In certain embodiments, electron transfer agents have structures orcharges which prevent or substantially reduce the diffusional loss ofthe electron transfer agent during the period of time that the sample isbeing analyzed. For example, electron transfer agents include but arenot limited to a redox species, e.g., bound to a polymer which can inturn be disposed on or near the working electrode. The bond between theredox species and the polymer may be covalent, coordinative, or ionic.Although any organic, organometallic, or inorganic redox species may bebound to a polymer and used as an electron transfer agent, in certainembodiments the redox species is a transition metal compound or complex,e.g., osmium, ruthenium, iron, and cobalt compounds or complexes. Redoxspecies described for use with a polymeric component may also be usedwithout a polymeric component.

A type of polymeric electron transfer agent that may be used with thedermal sensors contains a redox species covalently bound in a polymericcomposition, as described, e.g., in U.S. Pat. Nos. 6,605,200 and6,605,201, the disclosures of which are incorporated herein by referencein their entireties for all purposes. An example of this type ofmediator is poly(vinylferrocene). Another type of electron transferagent contains an ionically-bound redox species. This type of mediatormay include a charged polymer coupled to an oppositely charged redoxspecies. Examples of this type of mediator include a negatively chargedpolymer coupled to a positively charged redox species such as an osmiumor ruthenium polypyridyl cation. Another example of an ionically-boundmediator is a positively charged polymer such as quaternizedpoly(4-vinyl pyridine) or poly(1-vinyl imidazole) coupled to anegatively charged redox species such as ferricyanide or ferrocyanide.In other embodiments, electron transfer agents include a redox speciescoordinatively bound to a polymer. For example, the mediator may beformed by coordination of an osmium or cobalt 2,2′-bipyridyl complex topoly(l-vinyl imidazole) or poly(4-vinyl pyridine).

Suitable electron transfer agents are osmium transition metal complexeswith one or more ligands, each ligand having a nitrogen-containingheterocycle such as 2,2′-bipyridine, 1,10-phenanthroline, 1-methyl,2-pyridyl biimidazole, or derivatives thereof. The electron transferagents may also have one or more ligands covalently bound in a polymer,each ligand having at least one nitrogen-containing heterocycle, such aspyridine, imidazole, or derivatives thereof. An example of an electrontransfer agent includes (a) a polymer or copolymer having pyridine orimidazole functional groups and (b) osmium cations complexed with twoligands, each ligand containing 2,2′-bipyridine, 1,10-phenanthroline, orderivatives thereof, the two ligands not necessarily being the same.Some derivatives of 2,2′-bipyridine for complexation with the osmiumcation include but are not limited to 4,4′-dimethyl-2,2′-bipyridine andmono-, di-, and polyalkoxy-2,2′-bipyridines, such as4,4′-dimethoxy-2,2′-bipyridine. Derivatives of 1,10-phenanthroline forcomplexation with the osmium cation include but are not limited to4,7-dimethyl-1,10-phenanthroline and mono, di-, andpolyalkoxy-1,10-phenanthrolines, such as4,7-dimethoxy-1,10-phenanthroline. Polymers for complexation with theosmium cation include but are not limited to polymers and copolymers ofpoly(1-vinylimidazole) (referred to as “PVI”) and poly(4-vinyl pyridine)(referred to as “PVP”). Suitable copolymer substituents of poly(l-vinylimidazole) include acrylonitrile, acrylamide, and substituted orquaternized N-vinyl imidazole, e.g., electron transfer agents withosmium complexed to a polymer or copolymer of poly(l-vinyl imidazole).

Embodiments may employ electron transfer agents having a redox potentialranging from about −200 mV to about +200 mV versus the standard calomelelectrode (SCE). The sensing layer may also include an enzyme which iscapable of catalyzing a reaction of the analyte. The enzyme may also, insome embodiments, act as an electron transfer agent. One example of asuitable enzyme is an enzyme which catalyzes a reaction of the analyte.For example, an enzyme, such as a glucose oxidase, glucose dehydrogenase(e.g., pyrroloquinoline quinone (PQQ) dependent glucose dehydrogenase,flavine adenine dinucleotide (FAD) dependent glucose dehydrogenase, ornicotinamide adenine dinucleotide (NAD) dependent glucosedehydrogenase), may be used when the analyte of interest is glucose. Alactate oxidase or lactate dehydrogenase may be used when the analyte ofinterest is lactate. Laccase may be used when the analyte of interest isoxygen or when oxygen is generated or consumed in response to a reactionof the analyte.

In certain embodiments, an enzyme may be attached to a polymer, crosslinking the enzyme with another electron transfer agent (which, asdescribed above, may be polymeric). A second enzyme may also be used incertain embodiments. This second enzyme may be used to catalyze areaction of a product compound resulting from the catalyzed reaction ofthe analyte. The second enzyme may operate with an electron transferagent to electrolyze the product compound to generate a signal at theworking electrode. Alternatively, a second enzyme may be provided in aninterferent-eliminating layer to catalyze reactions that removeinterferents.

Certain embodiments include a sensing layer that works at a gentleoxidizing potential, e.g., a potential of about +40 mV. This sensinglayer uses an osmium (Os)-based mediator designed for low potentialoperation and is stably anchored in a polymeric layer. Accordingly, incertain embodiments the sensing element is redox active component thatincludes (1) Osmium-based mediator molecules attached by stable(bidente) ligands anchored to a polymeric backbone, and (2) glucoseoxidase enzyme molecules. These two constituents are crosslinkedtogether. Such sensing layers are described in, for example, U.S. Pat.No. 5,262,035, which is incorporated herein by reference in its entiretyfor all purposes.

Mass Transport Limiting Layer

The sensor may include a mass transport limiting layer (not shown),e.g., an analyte flux modulating layer, to act as a diffusion-limitingbarrier to reduce the rate of mass transport of the analyte, forexample, glucose or lactate, into the region around the workingelectrode. The mass transport limiting layers are useful in limiting theflux of an analyte to a working electrode in an electrochemical sensorso that the sensor is linearly responsive over a large range of analyteconcentrations and is easily calibrated. Mass transport limiting layersmay include polymers and may be biocompatible. A mass transport limitinglayer may serve many functions, e.g., functionalities of a biocompatiblelayer and/or interferent-eliminating layer may be provided by the masstransport limiting layer.

In certain embodiments, a mass transport limiting layer is a membranecomposed of crosslinked polymers containing heterocyclic nitrogengroups, such as polymers of polyvinylpyridine and polyvinylimidazole.Embodiments also include membranes that are made of a polyurethane, orpolyether urethane, or chemically related material, or membranes thatare made of silicone, silicone elastomer, and the like.

According to certain embodiments, a membrane is formed by crosslinkingin situ a polymer, modified with a zwitterionic moiety, a non-pyridinecopolymer component, and optionally another moiety that is eitherhydrophilic or hydrophobic, and/or has other desirable properties, in analcohol-buffer solution. The modified polymer may be made from aprecursor polymer containing heterocyclic nitrogen groups. For example,a precursor polymer may be polyvinylpyridine or polyvinylimidazole.Optionally, hydrophilic or hydrophobic modifiers may be used to“fine-tune” the permeability of the resulting membrane to an analyte ofinterest. Optional hydrophilic modifiers, such as poly(ethylene glycol),hydroxyl or polyhydroxyl modifiers, may be used to enhance thebiocompatibility of the polymer or the resulting membrane. Masstransport limiting layers that may be adapted for use wityh presentdisclosure are described, e.g., in U.S. Pat. No. 6,932,894, thedisclosure of which is incorporated herein by reference in its entiretyfor all purposes.

Accuracy

According to certain embodiments, analyte concentrations as determinedby the signals detected from a dermal analyte sensor according to thepresent disclosure are within 80% of a reference value, such as within85% of the reference value, including within 90% of the reference value,or within 95% of the reference value, or within 97% of the referencevalue, or within 98% of the reference value, or within 99% of thereference value. For example, for a given sensor, at least 80% ofanalyte signal from the sensor collected over a 14 day wear period arewithin 80% of a reference value as determined by a standard referencesuch as an in vitro test strip or YSI for glucose.

A high number of analyte concentrations as determined by the signalsdetected from a dermal analyte sensor are within Zone A of the ClarkeError Grid Analysis. For example, analyte concentrations as determinedby the signals detected from a dermal analyte sensor are within Zone Aof the Clarke Error Grid Analysis for 75% or more of the analytesensors, such as 80% or more, or 90% or more, including 95% or more, or97% or more, or 99% or more of the analyte sensors. In certaininstances, concentrations as determined by the signals detected from thedermal analyte sensor that are within Zone A or Zone B of the ClarkeError Grid Analysis. For example, dermal analyte concentrations asdetermined by the signals detected from the analyte sensor that arewithin Zone A or Zone B of the Clarke Error Grid Analysis for 75% ormore of the analyte sensors, such as 80% or more, or 90% or more,including 95% or more, or 97% or more, or 99% or more of the analytesensors.

Calibration

Due at least in part to the stability and accuracy of the dermalsensing, the sensors may require no calibration or no user calibrationafter being positioned in the dermal layer, or no more than onecalibration after positioned in the dermal layer. For example, a sensormay be factory calibrated and need not require further calibrating oncedermally positioned. In certain embodiments, calibration may berequired, but may be done without user intervention, i.e., may beautomatic. In those embodiments in which calibration by the user isrequired, the calibration may be according to a predetermined scheduleor may be dynamic, i.e., the time for which may be determined by thesystem on a real-time basis according to various factors, such as butnot limited to glucose concentration and/or temperature and/or rate ofchange of glucose, etc.

Methods of Manufacturing Sensor Applicator Sets and Dermal AnalyteSensors

Embodiments of the present disclosure relate to methods of manufacturingdermal analyte sensors, devices containing these sensors, and dermalsensor applicator sets. The methods include disposing an insertionneedle configured for dermal sensor insertion at an angle relative to adermal sensor that includes a working electrode such that, duringoperation of the applicator set, the insertion needle creates aninsertion path for the sensor as the sensor is being inserted into asubject.

In certain aspects, the dermal sensor is injection-molded from a plastic(e.g., a conductive plastic). A mold for the sensor may be designed toproduce a sensor having any of the sensor dimensions described. The moldmay further be designed to include shapes extending into or away from aninternal cavity of the mold that, upon completion of the moldingprocess, will result in the sensor having one or more structuralfeatures including, but not limited to, a groove having a shape and/orangle complementary to the insertion needle, a recess in which sensingreagent may be disposed, or any other structural feature that mayimprove the performance of (or provide additional functionalities to) ananalyte sensor employing the sensor. Once the mold is designed andproduced, the injection-molded sensor may be manufactured by heating athermoplastic, thermosetting plastic, and/or any other material suitablefor injection molding, injecting the heated material into the mold, andallowing the material to cool and harden to the configuration of thecavity. The molded sensor may then be retrieved from the mold, e.g., bydisassembling the mold into two or more component parts.

According to certain embodiments, a dermal analyte sensor is an extrudedsensor. That is, the sensor may be formed by coextruding a firstconductive material, a second conductive material, and a dielectricmaterial such that an extruded sensor having the first conductivematerial and the second conductive material electrically isolated by thedielectric material is formed. Extruded sensors and methods ofmanufacturing that may be adapted for use with the present disclosureare described in U.S. Patent Publication No. 2010/0326842, thedisclosure of which is incorporated herein by reference in its entiretyfor all purposes.

In other aspects, provided by the present disclosure are methods ofmanufacturing a dermal sensor that includes a working electrode. Themethods include forming a dermal sensor having a dermal insertion length(the length of the dermal sensor that resides in the dermal space whenthe sensor is operatively positioned) of from 0.5 mm to 3 mm (e.g., from1 mm to 2 mm), and disposing at least a first conducting material on allor a portion of the sensor, but at least at the dermal insertion lengthportion of a dermal sensor. In certain aspects, the methods furtherinclude disposing a second conducting material on all or a portion ofthe first conducting material. The first material (and when present, thesecond or more conductive materials) of conducting material mayindependently include a material selected from gold, carbon, platinum,ruthenium, palladium, silver, silver chloride, silver bromide, andcombinations thereof

Dermal sensors can be processed by punching a film of two or moreelectrically isolated conducting materials to form a sensor. Accordingto this embodiment, a film that is an electrically isolated bi-layer (ortri layer, quad layer, etc.) may be formed where there is a layer ofcarbon-doped polymer followed by a layer of dielectric polymer and thena layer of carbon-doped polymer that is further doped with platinum orother suitable conducting material). This film can then be punched inthe desired sensor shape and, optionally, laser machined to reveal oneor more inner layers similar to a printed circuit board. In certainembodiments, a suitable polymer is doped with sensing reagents toobviate the need to dispense sensing reagents on the sensor/electrodesin an additional manufacturing step.

Experimental Dermal Glucose Measurements Using Microprojection DermalElectrodes

All three electrodes of a dermal glucose sensor were positioned in thedermal layer and no further. Another sensor was also used in which justa working electrode of a dermal sensor was positioned in the dermallayer and no further, and the reference and counter electrodes of thissensor were positioned in the subcutaneous space. The working electrodesof each sensor were fabricated as shown and described in FIG. 2. Thereference electrodes and the counter electrodes were fabricated bycoating Au-coated substrates with either Ag/AgCl to form a referenceelectrode, or carbon to form a counter electrode.

Wires attached to a potentiostat were attached to the base of theworking electrode-bearing dermally implanted structure, as well assubcutaneously positioned counter and reference electrodes. A very smallhole was made in the skin of the arm using a lancet. The dermal workingelectrode structure was carefully inserted into the hole just to thedermal layer and no farther, and adhered to the skin with adhesive. Thecorresponding reference and counter electrodes were inserted into thesubcutaneous fat, to a depth of about 5 mm. As a control, a conventionalthree electrode subcutaneously positioned, transcutaneous in vivoglucose sensor was implanted in the arm adjacent to the dermal sensor,but all electrodes were in the subcutaneous layer.

Data was obtained simultaneously over a period of three days from boththe dermal and subcutaneous sensors.

Results are shown in FIG. 7, Panel A. The results shown are thoseobtained from the dermal sensor in which the working electrode waspositioned in the dermal space and the reference and counter electrodeswere positioned in the subcutaneous space. Results obtained from thesensor in which three electrodes were positioned in the dermal spacewere similar. The graph of FIG. 7 shows results of day three of a threeday simultaneous dermal/subcutaneous sensor experiment, with themeasured current from the dermal sensor (DS) shown on the left axis andthe measured current from the subcutaneous sensor (SC) on the rightaxis. The dermal sensor (solid line) leads the subcutaneous sensor(dashed line) by 5-8 minutes, depending on the peak. This is seen moreclearly when expanding the data, as shown in FIG. 7, Panel B. For thepeak on the left, at about 12:30 pm, the dermal sensor at 1 mm depthleads the subcutaneous sensor at 5 mm depth by about 7 minutes.Subsequent laboratory tests confirmed that the two sensors hadapproximately equal response times in-vitro, so the difference reflectsthe inherent differences between dermal sensors/sensing and subcutaneoussensors/sensing.

Although the foregoing subject matter has been described in some detailby way of illustration and example for purposes of clarity ofunderstanding, it is readily apparent to those of ordinary skill in theart in light of the present teachings that certain changes andmodifications may be made thereto without departing from the spirit orscope of the appended claims.

Accordingly, the preceding merely illustrates the principles of thedevices and methods described herein. It will be appreciated that thoseskilled in the art will be able to devise various arrangements which,although not explicitly described or shown herein, embody the principlesof the present subject matter and are included within its spirit andscope. Furthermore, all examples and conditional language recited hereinare principally intended to aid the reader in understanding theseprinciples and the concepts contributed by the inventors to furtheringthe art, and are to be construed as being without limitation to suchspecifically recited examples and conditions. Moreover, all statementsherein reciting principles, aspects, and embodiments of the presentsubject matter as well as specific examples thereof, are intended toencompass both structural and functional equivalents thereof.Additionally, it is intended that such equivalents include bothcurrently known equivalents and equivalents developed in the future,i.e., any elements developed that perform the same function, regardlessof structure. The scope of the present subject matter, therefore, is notintended to be limited to the exemplary embodiments shown and describedherein, but rather by the claims submitted herewith and in the future.

1-20. (canceled)
 21. A method of using an assembly to sense an analytelevel of a subject, the assembly comprising a base, an insertion needle,and a sensor, the method comprising: inserting a tip portion of aninsertion needle and a tip portion of a sensor, together, into a layerof a skin site of a subject such that the sensor is not inserted beyondthe subcutaneous layer, wherein a longitudinal central axis along thetip portion of the insertion needle is angled relative to a longitudinalcentral axis along the tip portion of the sensor and the tip portion ofthe insertion needle creates an insertion path for the sensor as theinsertion needle is inserted into the skin site; and sensing an analytelevel in the skin site with the sensor.
 22. The method of claim 20,wherein the longitudinal central axis along the tip portion of theinsertion needle is disposed at an angle relative to the longitudinalcentral axis along the sensor, wherein the angle is selected from thegroup consisting of 7° to 15°, 9° to 13°, and 5° to 20°.
 23. The methodof claim 20, wherein a distal portion of the sensor comprises a groovehaving a shape complementary to the insertion needle.
 24. The method ofclaim 20, wherein inserting the sensor comprises inserting a sensingregion of a working electrode of the sensor to a depth relative to anexternal skin surface of the subject, wherein the depth is selected fromthe group consisting of 0.5 mm to 3 mm and 1 mm to 2 mm.
 25. The methodof claim 20, wherein the tip portion of the insertion needle isnon-bladed.
 26. The method of claim 225, wherein the tip portion of theinsertion needle has a pointed termination on the longitudinal centralaxis of the insertion needle.
 27. The method of claim 226, wherein thetip portion of the insertion needle does not have an internal space. 28.The method of claim 20, wherein an inserted portion of the sensor has alength selected from the group consisting of between 0.5 mm and 3 mm andbetween 1 mm and 2 mm.
 29. The method of claim 20, wherein a distal endof the sensor comprises a molded recess to accept analyte-sensingreagents.
 30. The method of claim 20, wherein the insertion needle isadjacent to the sensor in a side-by-side arrangement.
 31. The method ofclaim 20, wherein the insertion needle and the sensor are inserted at anon-normal angle to the skin site.
 32. The method of claim 20, whereinthe sensor is inserted into but not through a dermal layer of the skinsite.
 33. The method of claim 20, wherein the sensor is inserted into asubcutaneous tissue of the skin site.
 34. An assembly, comprising: asensor having a distal portion, the sensor being configured to sense ananalyte level in a subcutaneous layer of a skin of the subject; aninsertion needle having a tip portion characterized in that alongitudinal central axis along the tip portion is in a convergingangled relationship with a longitudinal axis along the sensor, such thatthe insertion needle contacts or comes close to the distal portion ofthe sensor; and a base coupled with the insertion needle and the sensor,wherein the insertion needle is configured to create an insertion pathfor the sensor while in the angled relationship such that the sensor maybe inserted into but not through the subcutaneous layer when theinsertion needle and the sensor are inserted into the skin.
 35. Theassembly of claim 34, wherein the insertion needle is configured to beremovable from the subcutaneous layer while the sensor is in thesubcutaneous layer.
 36. The assembly of claim 34, wherein thelongitudinal central axis along the tip portion of the insertion needleis disposed at an angle relative to the longitudinal central axis alongthe sensor, wherein the angle is selected from the group consisting of7° to 15°, 9° to 13°, and 5° to 20°.
 37. The assembly of claim 34,wherein the sensor comprises a sensing region of a working electrodeinsertable to a depth of 3 mm to 10 mm.
 38. The assembly of claim 34,wherein the tip portion of the insertion needle is not hollow.
 39. Theassembly of claim 34, wherein the tip portion of the insertion needleand the distal portion of the sensor are co-localized such that a singlecontact point for the insertion needle and distal portion of the sensorresults at the surface of the skin.
 40. The assembly of claim 34,wherein both the insertion needle and the sensor are configured to beinsertable at a non-normal angle to the skin.